1. Field of the Invention
The present invention relates to gas chromatograph devices, and specifically pertains to a compact improved gas chromatograph device for "on line" use in combination with absorption spectrum analyzers, particularly, infrared spectrometers.
2. Description of the Prior Art
Chromatograph elution of a mixture of sample vapors is a common laboratory procedure. The separated sample components issue from the chromatograph column at a rate determined by many factors, among which is the carrier gas flow velocity. The efficiency of the chromatographic separation is dependent upon operation of the column at, or very near, the optimum carrier gas velocity for the given column conditions. The most efficient chromatographs emit well spaced eluted sample mixture components characterized by narrow peak widths as shown on chromatograph charts. That is, eluted samples are preferably issued from the chromatograph column in the briefest time interval measured from leading edge to trailing edge of peak.
On the other hand, absorption spectrum analyzers require a fixed, and in a given spectrometer, an irreducible period of time to scan the sample through the selected frequency range, process and record the resultant data. The infrared spectrometer is, at present, the most widely used laboratory chemical identification absorption spectrum analyzer.
The time of response of presently available infrared spectrometers is approximately an order of magnitude longer than the presently available efficient gas chromatograph output peak transit time. As a consequence, these two instruments are not normally compatible when directly connected one to another, but may be used in combination for the separation and identification of chemical compounds only by skillful and time consuming manipulations performed by qualified technicians. Previous practice has comprised catching and storing in separate sample cells the eluted sample peaks issuing from a chromatograph column, then placing the separate sample cells, one by one, in the spectrometer for the required time to complete the spectrometer analysis. "On line" operation of a gas chromatograph in combination with an absorption spectrum analyzer, such as an infrared spectrometer, has for full spectrum range analysis, not been feasible to this date.
Because of the cumbersome procedures for wide frequency band absorption spectrum analysis of eluted samples, a practice referred to as analysis, "on the fly" has been developed. The eluted sample peak is passed through the spectrometer "on the fly" and absorption spectra data is recorded, as may be obtained in the brief interval of time the sample material requires to pass the windows of a flow through sample cell. An experienced analytical chemist can utilize the fragmentary absorption spectrum "fly" data to provide useful sample compound identification clues. The "fly" spectrometer analysis is a compromise and a limited value substitute for the full frequency spectrum scan analysis.
Additional problems attend present practices for combining gas chromatographic devices with absorption spectrum spectrometers, particularly, infrared spectrometers. Sample compounds issue from chromatograph columns at elevated temperatures. Present chromatographs require bulky ovens and temperature control paraphernalia. The higher temperatures of the chromatograph, if mounted adjacent to an infrared spectrometer without special heat shielding, would interfere with the operation of the spectrometer.
It is common practice to operate gas chromatograph columns at programmed elevated temperatures selected to assure proper volatility of all elutant sample components. Abrupt temperature changes of elutants, as these issue from a chromatograph column and are caught and stored temporarily in sample cell containers awaiting spectrometer analysis, may give rise to altered physical states of the eluted samples. Rapid cooling of eluted samples may result in condensation on the sample cell windows. All of the foregoing effects adversely degrade the absorption spectrum analysis data.
Reduction in the number of required hand manipulations of toxic and dangerous materials during analysis and production quality control procedures is an important safety advantage. No presently available gas chromatograph provides compatible means for matching the chromatograph output directly with an infrared spectrometer. As a consequence, dangerous toxic elutants must be hand transferred from the chromatograph output to a spectrometer sample cell. After the spectrum analysis is completed, the toxic sample contents of the sample cell must be cleared. All these presently required steps involve separate hand manipulations and incur some element of hazard. Continuous "on stream" management of dangerous materials significantly reduces the risks of loss or dispersion of toxic sample materials.
The incompatibility of presently available gas chromatographs and infrared spectrometers is not only limited to time incompatibility. The shear size and vertical dimensions of present chromatographs, as compared with spectrometer sample cell dimensions, makes the direct physical matching of chromatograph output to spectrometer sample cell apparatus awkward. The different ambient temperature requirements for operation of the two kinds of instruments, as referred to above, further complicates "on line" matching of presently available chromatographs and infrared spectrometers.
The chromatograph column emits large volumes of gaseous effluent, some of which may be combined with portions of reactive corrosive sample mixture vapors. Infrared spectrometers are sensitive complex instruments easily damaged by corrosive chemicals. Direct physical combination of the output of gas chromatograph devices with infrared and other absorption spectrum spectrometers in the absence of special precaution, risks corrosion and damage to sensitive spectrometer working parts.
There is, accordingly, a need for a gas chromatograph device that may be conveniently and compatibly combined directly with absorption spectrum analyzer equipment. Particularly, there is a present need for a compact easily operated gas chromatograph suitable for "on line" combination with infrared spectrometers.